The present invention relates to a measurement system, and relates particularly to a measurement system that performs measurements to determine the form of a work being processed.
Conventionally, measurements made to determine the form of a work being processed are performed using a laser measurement instrument. Specifically, the laser measurement instrument is located where the surface of an entire work being processed can be scanned, and the scanning of the surface is performed using a laser beam. Then, distances between the measurement instrument and measurement points on the surface of the work being processed are calculated to obtain measurements to determine the form of the work being processed.
An example laser measurement instrument has the following arrangement (see, for example, patent document 1): a measurement light emitting unit, for emitting a laser beam that strikes an object to be measured; a light receiving unit, for receiving light reflected by the object to be measured; and a distance calculation unit, for employing the laser beam that is emitted and the reflected light that is received to calculate a distance to the object to be measured.
However, according to the arrangement disclosed in patent document 1, since the optical paths differ for the laser beam emitted by the laser measurement instrument, and the light reflected by the object to be measured and returned to the laser measurement instrument, a complicated arrangement is required for the laser measurement instrument.
To resolve this problem, the following, example laser instrument is proposed.
FIG. 2 is a schematic diagram illustrating the proposed arrangement for a laser measurement instrument 100.
The laser measurement instrument 100 includes: a half mirror 10, also called a semi-transmitting mirror, a measurement light emitting unit 11, a projection unit 12, a light receiving unit 13 and a distance calculation unit 14, and a case 15 in which these components are stored.
As light for performing measurements, the measurement light emitting unit 11 emits a laser beam that passes through the half mirror 10.
The projection unit 12 is, for example, a lens for guiding the laser beam, which is emitted by the measurement light emitting unit 11 and passes through the half mirror 10, to an object being measured, and for guiding to the half mirror 10 the laser beam that is reflected from the object to be measured.
The light-receiving unit 13 receives, from the object to be measured, the reflected laser beam, which reaches the half mirror 10 through the projection unit 12 and is reflected on the half mirror 10.
The distance calculation unit 14 employs the timing for a period, extending from the time the laser beam is first emitted by the measurement light emitting unit 11 until the reflected light, from the object to be measured, is received by the light receiving unit 13, to calculate the distance from the laser measurement instrument 100 to the object to be measured.
According to the laser measurement instrument 100, and in consonance with the solid lines shown in FIG. 2, when the measurement light emitting unit 11 emits the laser beam directed toward the half mirror 10, the laser beam passes through the half mirror 10 and the projection unit 12 and impinges on the object to be measured. Thereafter, the laser beam reflected by the object to be measured is transmitted, through the projection unit 12 again, and returned to the half mirror 10 and is reflected there, and the reflected light is received by the light-receiving unit 13. Then, the distance calculation unit 14 measures the time required for the period extending from the emission of the laser beam to the reception of the reflected laser beam, and from this, obtains the distance from the laser measurement instrument to the object to be measured.    [Patent Document 1] JP-A-62-127685
When the measurement light emitting unit 11 emits a laser beam directed towards the half mirror 10, nearly all the light passes through the half mirror 10 and continues on to the projection unit 12; however, as indicated by a broken line in FIG. 2, not all the light passes through the half mirror 10, part is reflected and follows a path towards an inner wall of the case 15. At the inner wall of the case 15, the laser beam reflected on the half mirror 10 is again reflected and is returned to and passes through the half mirror 10, and reaches the light-receiving unit 13.
Therefore, since the light-receiving unit 13 receives both laser beam reflected by an object to be measured and laser beam reflected by the inner wall of the case 15, the light reflected by the inner wall of the case 15 becomes noise, and this adversely affects the accuracy of a result obtained by the distance calculation unit 14. As a result, an error occurs in the measurement of the distance from the laser measurement instrument 100 to the object to be measured.